Synthesis, Coordination Properties, and Catalytic Use of Phosphinoferrocene Carboxamides Bearing Donor-Functionalized Amide Substituents

Synthesis and coordination of hybrid phosphinoferrocenes with extended donor pendants

Combining a phosphinoferrocene fragment with extended multidonor moieties affords novel, flexible multidonor pro-ligands. This contribution describes the synthesis of two structurally similar functional phosphines, Ph₂PfcNHC(O)CH₂PPh₂ (1) and Ph₂PfcNHCH₂CH₂PPh₂ (2, fc = ferrocene-1,1'-diyl), and their coordination behaviour towards Pd(II). The former amidophosphine reacts with [PdCl₂(MeCN)₂] to produce the chelate complex [PdCl₂(1-κ²P,P')] as a mixture of cis and trans isomers, which convert into bis-chelate [PdCl₂(Ph₂PfcNC(O)CH₂PPh₂-κ³P,P',N)] upon reacting with a strong base (KOt-Bu). In contrast, the more flexible and more basic phosphinoamine 2 directly forms the cationic bis-chelate complex [PdCl(2-κ³P,P',N)]Cl via spontaneous self-ionisation. Subsequent halogen abstraction with Ag[SbF₆] results either in counter ion exchange to give [PdCl(2-κ³P,P',N)][SbF₆] or in the formation of a structurally unique complex [PdCl(2-κ⁴Fe,P,P',N)][SbF₆]₂ with an Fe → Pd dative interaction, depending on the amount of silver(I) salt used (1 or 2 equiv.).

Versatile coordination and C-H activation of a multi-donor phosphinoferrocene carboxamide ligand in Pd(ii) complexes

A multi-donor phosphinoferrocene carboxamide, FcCONHCH₂CH₂PPh₂ (1, Fc = ferrocenyl), was prepared, converted into the corresponding phosphine oxide 1O and phosphine selenide 1Se and, mainly, studied as a ligand in Pd(ii) complexes. In its native form, amide 1 preferentially coordinated soft Pd(ii) as a simple phosphine, giving rise to mixtures of cis and trans-[PdX₂(1-κP)₂] (2; X = Cl (a), Br (b), and I (c)), wherein the isomer ratios depended on the auxiliary halide ligand or, alternatively, to the complex [(L^NC)PdCl(1-κP)] (6, L^NC = 2-[(dimethylamino)methyl-κN]phenyl-κC¹). This coordination mode was nevertheless easily changed when creating a vacant coordination site at the palladium. Thus, treatment of 2a with NH₄[PF₆] in the presence of free 1 produced [PdCl(1-κP)₃][PF₆] (3), while complete halogen removal with a Ag(i) salt led to cationic complexes cis-[Pd(1-κ²O,P)₂]X₂ (4, X = CF₃SO₃ (a), ClO₄ (b), BF₄ (c)) or [(L^NC)Pd(1-κ²O,P)]X (7a and 7b), containing seven-membered O,P-chelate rings. In contrast, amide nitrogen deprotonation with KOt-Bu followed by spontaneous intramolecular halogen substitution resulted in the transformation of 6 into the chelate complex [(L^NC)Pd{(1- H)-κ²N,P}] (8) featuring a five-membered N,P-chelate ring, and in the conversion of 2a and 2b into the product of C-H bond activation [Pd{Fe(η⁵-C₅H₃CONCH₂CH₂PPh₂-κ³C,N,P)(η⁵-C₅H₅)}(1-κP)] (5), with doubly chelating deprotonated 1. Importantly, complexes 2-4-5 and 6-7-8 were mutually interconverted in triads (by protonation/deprotonation and by halide addition/abstraction), which highlights the flexible coordination and chemical stability of ligand 1. The crystal structures of 1O·½H₂O, trans-2a·MeCN, trans-2b·3C₂H₄Cl₂, trans-2c·2.5C₂H₄Cl₂, 4a·CH₂Cl₂, 5·3CHCl₃·Et₂O, and 8 were determined by single-crystal X-ray diffraction analysis, and the representative compounds were studied by cyclic voltammetry.

Synthesis and characterization of 1'-(diphenylphosphino)-1-isocyanoferrocene, an organometallic ligand combining two different soft donor moieties, and its Group 11 metal complexes

The development of a practical synthesis of 1'-(diphenylphosphino)-1-aminoferrocene (2) and its P-borane adduct (2B) allowed the facile preparation of 1'-(diphenylphosphino)-1-isocyanoferrocene (1). This compound combining two specific soft-donor moieties was studied as a ligand for univalent Group 11 metal ions. The reactions of 1 with AgCl at 1 : 1 and 2 : 1 molar ratios only led to the coordination polymer [Ag₂(μ-Cl)₂(μ(P,C)-1)]_n (6), while those with Ag[SbF₆] provided the dimer [Ag₂(Me₂CO-κO)₂(μ(P,C)-1)₂][SbF₆]₂ and the quadruply-bridged disilver complex [Ag₂(μ(P,C)-1)₄][SbF₆]₂ (8), respectively. Addition of 1 to [AuCl(tht)] (tht = tetrahydrothiophene) afforded the mono- and the digold complex, [AuCl(1-κP)] (9) and [(μ(P,C)-1)(AuCl)₂] (10), depending on the reaction stoichiometry. Finally, the reaction of 1 with [Au(tht)₂][SbF₆] or halogenide removal from 9 with AgNTf₂ led to cationic dimers [Au₂(μ(P,C)-1)₂]X₂ (11, X = SbF₆ (a) or NTf₂ (b)). Catalytic tests in the Au-mediated isomerization of (Z)-3-methylpent-2-en-4-yn-1-ol to 2,3-dimethylfuran revealed that 11a and 11b are substantially less catalytically active than their analogues containing 1'-(diphenylphosphino)-1-cyanoferrocene as the ligand, most likely due to a stronger coordination of the isonitrile moiety, which prevents dissociation of the dimeric complexes into catalytically active monomeric species.

Synthesis of phosphinoferrocene amides and thioamides from carbamoyl chlorides and the structural chemistry of Group 11 metal complexes with these mixed-donor ligands

The reaction of in situ generated 1'-(diphenylphosphino)-1-lithioferrocene with carbamoyl chlorides, ClC(E)NMe2, affords the corresponding (thio)amides, Ph2PfcC(E)NMe2 (E = O (), S (); fc = ferrocene-1,1'-diyl). These compounds as well as their analogues, Ph2PfcC(O)NHMe () and Ph2PfcC(O)NH2 (), prepared from 1'-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) were studied as ligands for the Group 11 metal ions. In the reactions with [Cu(MeCN)4][BF4], the amides give rise to bis-chelate complexes of the type [Cu(L-κ(2)O,P)2][BF4]. Similar products, [Ag(L-κ(2)O,P)2]ClO4, are obtained from silver(i) perchlorate and , or . In contrast, the reaction of AgClO4 with produces a unique molecular dimer [Ag()(ClO4-κO)]2, where the metal centres are bridged by the sulfur atoms of the P,S-chelating thioamides. The reactions of with [AuCl(tht)] (tht = tetrahydrothiophene) afford the expected gold(i)-phosphine complexes, [AuCl(L-κP)], containing uncoordinated (thio)amide moieties. Hemilabile coordination of the phosphinoamide ligands in complexes with the soft Group 11 metal ions is established by the crystal structure of a solvento complex, [Cu(-κ(2)O,P)(-κP)(CHCl3-κCl)][BF4], which was isolated serendipitously during an attempted crystallisation of [Cu(-κ(2)O,P)2][BF4]. All of the compounds are characterised by spectroscopic methods, and the structures of several representatives of both the free phosphinoamides and their complexes are determined by X-ray diffraction analysis and further studied by DFT calculations and cyclic voltammetry.